<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        * {
            margin: 0;
            padding: 0;
        }

        ul {
            list-style: none;
        }

        .wrap {
            width: 330px;
            height: 30px;
            margin: 100px auto 0;
            padding-left: 10px;
            background-image: url(imgs/bg.jpg);
        }

        .wrap li{
            background-image: url(imgs/libg.jpg);
        }

        .wrap > ul > li {
            float: left;
            margin-right: 10px;
            position: relative;
        }

        .wrap a {
            display: block;
            height: 30px;
            width: 100px;
            text-decoration: none;
            color: #000;
            line-height: 30px;
            text-align: center;
        }

        .wrap li ul {
            position: absolute;
            top: 30px;
            display: none;
        }

    </style>
    <script type="text/javascript" src="../jquery-1.11.1.min.js"></script>
    <script>
       $(function(){

           //鼠标移入事件
           $(".wrap > ul > li").mouseenter(function(){
               $(this).children("ul").show();
           })

           //当鼠标离开时，绑定鼠标离开事件
           $(".wrap > ul > li").mouseleave(function(){
               $(this).children("ul").hide();
           })
       })
    </script>
</head>
<body>
   <div class="wrap">
       <ul>
           <li>
               <a href="javascript:void(0);">一级菜单1</a>
               <ul>
                   <li><a href="javascript:void(0);">二级菜单1</a></li>
                   <li><a href="javascript:void(0);">二级菜单2</a></li>
                   <li><a href="javascript:void(0);">二级菜单3</a></li>
               </ul>
           </li>
           <li>
               <a href="javascript:void(0);">一级菜单2</a>
               <ul>
                   <li><a href="javascript:void(0);">二级菜单1</a></li>
                   <li><a href="javascript:void(0);">二级菜单2</a></li>
                   <li><a href="javascript:void(0);">二级菜单3</a></li>
               </ul>
           </li>
           <li>
               <a href="javascript:void(0);">一级菜单3</a>
               <ul>
                   <li><a href="javascript:void(0);">二级菜单1</a></li>
                   <li><a href="javascript:void(0);">二级菜单2</a></li>
                   <li><a href="javascript:void(0);">二级菜单3</a></li>
               </ul>
           </li>
       </ul>
   </div>
</body>
</html>